1. Field of the Invention
This invention relates generally to energy management, and in particular to air flow control in a heating, ventilating and air conditioning system (HVAC) by selective zone isolation.
2. Description of the Prior Art
Because of the rapidly rising costs of energy, the incentives to conserve are increasing, both for domestic users as well as industrial users. For most domestic users, home air conditioning and heating accounts for a substantial portion of the annual energy expense. Although most dwellings are insulated, a large amount of energy is expended by the air conditioning compressor to pump radiant heat absorbed by the dwelling structure out of the air conditioned living space to the outside ambient air. Likewise, a great deal of energy is expended by the furnace to replace heat energy which is lost through the walls and ceiling of the dwelling structure.
For energy conservation reasons, it is common practice to reduce the degree of cooling or heating during periods of minimum activity, for example at night, according to comfort requirements. For example, the ambient temperature in a home can be reduced at night while the occupants are asleep without causing any discomfort. Additionally, the temperature can be reduced substantially during the day when the dwelling is not occupied. Such reduction in the nighttime temperature of the dwelling is referred to as a "set-back" which results in a significant reduction in fuel consumption for heating and cooling the dwelling.
Although the night set-back thermostat provides energy savings, the air conditioning compressor or furnace is still subjected to the entire heat gain/loss loading of the dwelling, limited only by upward or downward (depending on the season) temperature drift through the entire home. Obvious comfort requirements restrict this drift and limits savings potential in many cases.
It has been common practice by homeowners to reduce energy costs by closing off certain rooms which are no longer in use. This is commonly carried out by closing the outlet vent of the supply duct for the room which is to be isolated. It will be appreciated that while this may be an acceptable method on a long term basis, it cannot be conveniently practiced on a daily basis. The requirement to manually close and open the vent is subject to human failure and neglect whereby cost savings are lost. Moreover, manual alteration of the vent opening is not entirely satisfactory since the isolated room will be uncomfortably cool or warm in the morning before its vent manually opened and, due to the lag time of typical heating and cooling systems, half an hour or more is usually required for room temperature to reach a comfortable level for normal daytime activities. Finally, most supply vents are located on the ceiling at an elevation which cannot be conveniently reached without the aid of a stepladder.
In some commercial installations, the flow of conditioned air through an air supply duct is regulated by a moveable damper plate. The position of the damper plate is established by a reversible drive motor as a function of air velocity through the supply duct and temperature of the air in the space being serviced. The mechanical damper assembly is not well suited for retrofit applications because of the extensive duct modification required and the expense of the damper motor and damper control. Moreover, the mechanical damper assembly is not suited for retrofit installations in some cases because of the lack of adequate working space around the supply ducts. Finally, the mechanical damper plate must have clearance along its edges to allow it to rotate within the damper. Thus, it cannot completely close off the air flow passage. In such installations, the mechanical damper plate modulates the conditioned air flow to accomodate temperature changes in the air space being serviced, rather than completely closing it off.